We employed S-to-P converted waveforms to detect mid-mantle scattering beneath northeastern China and the adjacent Japan Sea. Broadband and short-period waveforms recorded by seismic arrays for eight moderate-sized deep earthquakes were analyzed using a non-linear array stacking technique, and mid-mantle scatterers within the depth range 930-1120 km were clearly revealed. The heterogeneities have an overall lateral extent of ~800 km, and mostly occur within a region with a high velocity anomaly. The accumulation of MORB-like slab materials at mid-mantle depths might cause a different chemical composition than that of the surrounding peridotitic mantle. The spatial isolation of the heterogeneities from the stagnant Pacific slab suggests an origin related to the subduction of ancient Izanagi plate. In combination with the reconstruction history of plate motions, we estimate the viscosity of the topmost lower mantle to vary from 1.0 × 1022 to 1.6 × 1023 Pas, which can be used as an independent constraint on the rheology of the lower mantle on a regional scale.
Bibliographical noteFunding Information:
We thank Satoshi Kaneshima and an anonymous referee for valuable comments, which greatly improve the manuscript. Thanks are due to Gabriele Morra and Steven Jacobsen for some stimulating discussions. J. Li wants to thank Fenglin Niu for the inspired thoughts and talks. The manuscript is finished while J. Li visiting CU, Boulder, and she gratefully acknowledges the support of K.C. Wong Education Foundation, Hong Kong . We also thank IRIS and GRSN data centers for providing waveform data. GMT software was used for plotting most of the figures. This research was supported by NSFC (J. Li, Grants 41074034 and 41274065 ) and NSF geochemistry programs.
- Izanagi plate
- Mid-mantle discontinuity